It is important that the relationships between parts of the ontology are defined and applied consistently. However, the ontology must also be adaptable if it is to remain useable as circumstances change. For instance, new technical developments, or commercial or regulatory requirements, may require modification of a technical standard, or the definition of new relationships between its elements. For example, a mobile telephony standard originally developed to ensure interopability between handsets and fixed network components will require considerable adapation if a new requirement is introduced requiring a first network to support handsets of subscribers of a second network. In another example, classification systems for technical literature such as patents have to be kept abreast of developments in the technologies that are the subject of the classification, and this involves considerable workload to co-ordinate the behaviour of all the users of the classification system, from reporting of the need for such changes through to their consistent implementation.
There is a difficult balance to be struck between on the one hand keeping an ontology internally consistent, which is best met by maintaining a tight change-control system, administered by a small group of people, and on the other hand maintaining the ontology's usefulness by allowing any user who has an interest to initiate changes. The result is generally that any proposals for change have to be submitted to a slow and cumbersome committee process, considerably delaying the introduction of any proposal.
Ontology servers exist which provide a facility to share vocabularies and versioning systems between a number of users who have access to a set of data resources. Such ontology resources provide information on data schema and relationships between data schema.
A mechanism for collaboratively developing ontologies is specified by Farquhar, A.; Fikes. R.; & Rice, J. in an article “The Ontolingua Server: a Tool for Collaborative Ontology Construction”; published in the Proceedings of the Tenth Knowledge Acquisition for Knowledge-Based Systems Workshop; (Banff, Canada; Nov. 9-14, 1996). This provides tools that make use of the world-wide web to enable wide access and provide users with the ability to publish, browse, create, and edit ontologies stored on an ontology server. An individual user can therefore assemble a new ontology from a library of modules. However, there would be problems of consistency and validity of the ontology if a number of users were to attempt to collaborate in order to generate a common ontology that they can all use. If every user were given complete freedom to amend the common ontology, inexperienced or inconsiderate users might make changes which would cause considerable detriment to the usefulness of the ontology to the other users. If the reliability of the inputs is unknown, contradictory information or contradictory results of inference cannot be evaluated against each other. Therefore some moderation of the process is required. However, no individual human user, or group of such individuals, can be expected to have a full understanding of the needs of all the other users of the ontology, especially in a user group that is open to any user wishing to make use of it. A consultation process with all users, such as that proposed by Farquhar, Fikes, and Rice, delays implementation of any changes required, and would be very difficult to arrange, especially in the context of a real business environment, except with a closed community of relatively small size. There is therefore a need to control access to a shared data resource in order to maintain its quality without restraining the ability of users to contribute to that resource.